It's very strange, Lona, but logically, if it was a problem with the forum software, I would have expected a) for it to affect all threads you have posted in, and b) for it to have also affected other members. However, we know that odd things can happen from time to time, so I can't guarantee there isn't a glitch in your profile, but would be surprised if there is, given that Sam did the forum upgrade at the weekend, and this was happening before and after.
Unless Sam can come up with anything concrete, I can only suggest that when you get a notification email, click the link to stop the notifications, and see if that works. Obviously, if you are getting notifications from several threads, you would need to click the 'stop' link in all of them, as they arrive. Sorry I can't come up with any other answer.